This invention relates to system for drilling and fracturing subsurface formations and more particularly to such a system using millimeter-wave radiation energy.
There is a recognized need for a better technology for deep drilling into subsurface formations to access, for example, new sources of gas, oil and geothermal energy. Drilling at depths beyond 25,000 feet is increasingly difficult and costly using present rotary drilling methods.
Current rotary drilling technology is a slow grinding and fluid flushing process that has been in use for over 100 years. This drilling process is further slowed by the need to frequently withdraw the drill to replace drill bits, casing/cementing, and to make diagnostic measurements of the borehole, accounting for up to 50% of the drill time. Furthermore, drilling to penetration depths beyond 25,000 feet (7,620 m) can be extremely difficult and costly because of increasing temperature, pressure and decreasing mechanical torque efficiencies with increasing depth. Advances in ground boring technology over this current state of the art are needed to make access into the earth's subsurface easier, deeper, and less costly.
It is also recognized that fracturing is required in many deep underground formations to extend borehole access to deep underground energy sources, for example. It is a key element in enhanced geothermal systems to make possible the circulation of injected water into hot dry rock between injection and production wells to extract heat. Fracturing is also necessary to extract natural gas and petroleum from tight formations that are being increasingly accessed to meet growing energy demands. Currently there is a large market to stimulate natural gas and petroleum reservoirs using hydraulic fracturing.
Hydraulic fracturing, known in the prior art, uses a fluid under high pressure to cause fractures to open in subsurface strata. The maximum pressure that can be obtained is limited by the mechanical pumps used to pump the fluid. Getting at increasingly deeper and tighter formations is constrained by available mechanical pumping technology. In addition, large volumes of fluid are normally required. A typical fluid is water with chemical additives optimized for fracturing. This fluid is a source of pollution that can contaminate underground drinking water sources and surface areas when it is pumped out into surface reservoirs. Thus the fluid is a significant detrimental environmental issue for many locations that can prevent exploitation of some energy formations.
It is therefore an object of the present invention to provide technology for deep drilling and fracturing of subsurface formations. The approach disclosed herein can potentially increase the penetration rate for deep drilling by a factor of 10 to 100.